I use a 240 volt to 120 volt transformer for the fan and filament
transformer in my 3CX800 amplifier. Got it from Mouser. 3CX800s only draw
1.5 amps of fil current each.
73
Jim W7RY
On Sat, May 29, 2010 at 8:05 AM, Vic K2VCO <vic@rakefet.com> wrote:
> My amp project power supply has several 120v loads as well as the 240v
> plate transformer.
> They include a fan that draws about 100 mA, a screen supply that will take
> about 350 mA,
> and a filament transformer that will probably draw about 1A.
>
> The problem is how to connect the 120v loads. One solution is to just use a
> 4-wire circuit
> which will provide a neutral in addition to the two hot wires and ground.
> Then the 120v
> loads can be connected between the hot wires and the neutral.
>
> Another option is bridging the 120V loads across the two halves of the 240V
> plate
> transformer's primary. I've seen this done with fans, etc. The primary acts
> as an
> autotransformer to provide half voltage. Then I could use a simple 3-wire
> hookup.
>
> But I wonder how far I can go with this. If I put the filament transformer
> across one half
> and the screen supply across the other, would the unbalanced currents cause
> the voltage on
> the lightly loaded side to be excessive? This is a smallish amplifier --
> the plate
> transformer is about 1 kVA.
>
> Has anybody tried this?
>
> No, I am NOT thinking about using the ground as a neutral! If the bridging
> idea is
> impractical, I'll bite the bullet and put in a 4-wire circuit.
>
> --
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco/
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